The redistribution method plays an important role in addressing the issue of organosilicon by-product in the direct synthesis of dichlorodimethylsilane, and the redistribution mechanism is still a topic of debate. The redistribution by ZSM-5(3T)@γ-Al2O3 core-shell catalyst and post-modified AlCl3/ZSM-5(3T)@γ-Al2O3 catalyst was technically performed using the Density Functional Theory (DFT) at the level of B3LYP/6-311++G(3df,2pd). The result shows that No.1 active site of ZSM-5(3T)@γ-Al2O3 core-shell structure has a significant effect on the activity of the catalyst. Indicating that the active center involved in the reaction is H provided by Al-O-H bond, which is an obvious catalytic active center of Bronsted acid. Furthermore, post-modified AlCl3/ZSM-5(3T)@γ-Al2O3 catalyst is in more favor of redistribution reaction comparing with ZSM-5(3T)@γ-Al2O3 core-shell catalyst. It ascribes to the robust Lewis site of aluminum chloride favorable modification.
The structural, electronic, optical, and electrical properties of CuO were studied using the density functional theory (DFT) based on the Full Potential Linearized Augmented Plane Wave (FP-LAPW) method as implemented in the Wien2k code. The structural parameters are optimized by using the 4D-optimize option and the PBE-sol functional. The electronic and optical properties were analysed adopting Generalized Gradient approximation plus the screened Coulomb interaction (GGA+U) and the modified Becke-Johnson (GGA-TB-mBJ) potential for comparison. The calculated band energies have been used with the Boltzmann transport equation to calculate the thermoelectric properties. It is shown that the gap energy obtained by the (TB-mBJ) approximation potential is 2.02 eV more close to the experimental values comparing to that given by the GGA+U (Eg=1.57 eV). The optical properties reveal a high absorption coefficient in the UV region with an average transmittance of around 65% in the visible range, which covers a high range of light using TB-mBJ exchange potential and an average reflectivity of approximately 18% in visible light. The CuO conductivity is limited by the carrier mobility at low temperature and primarily defined by the carrier concentration at high temperature. These properties make CuO a promising material for solar cell applications as an absorbent layer and antireflection coating.
When computing the potential-energy curve of a diatomic molecule for predictive spectroscopy, high-level calculations are usually desired. The best calculations are expensive, so few points are usually available. The points are fitted to a continuous function, such as a polynomial. Ro-vibrational energy levels are then computed using the fitted function, and spectroscopic constants extracted. However, there may be problems with overfitting, with inadequate flexibility of the fitting function, or with dependence of results upon the choice of fitting function. More fundamentally, the fitting function is selected using aesthetics or convenience, instead of physics. Here we suggest using a lower-level, high-resolution ab initio potential as a guide. Instead of fitting the sparse, high-level data directly, the energy differences between the high-level points and the guiding potential are fitted. The results are improved even with an inexpensive guiding potential. This simple strategy involves little additional effort and can be recommended for routine use. It is similar to some interpolation strategies in the literature of polyatomic molecules. When the guiding potential extends beyond the high-level data, extrapolations are also improved.
The realization of fractional quantum chemistry is presented. Adopting the integro-differential operators of the calculus of arbitrary-order, we develop a general framework for the description of quantum nonlocal effects in the complex electronic environments. After a brief overview of the historical and fundamental aspects of the calculus of arbitrary-order, various classes of fractional Schrödinger equations are discussed and pertinent controversies and open problems around their applications to model systems are detailed. We provide a unified approach toward fractional generalization of the quantum chemical models such as Hartree-Fock and Kohn-Sham density functional theory and develop fractional variants of the fundamental molecular integrals and correlation energy. Furthermore, we offer various strategies for modeling static and dynamic quantum nonlocal effects through constant- and variable-order fractional operators, respectively. Possible directions for future developments of fractional quantum chemistry are also outlined.
Hexagonal chains are a special class of catacondensed benzenoid system and phenylene chains are a class of polycyclic aromatic compounds. Recently, A family of Sombor indices was introduced by Gutman in the chemical graph theory. It had been examined that these indices may be successfully applied on modeling thermodynamic properties of compounds. In this paper, we study the expected values of the Sombor indices in random hexagonal chains, phenylene chains, and consider the Sombor indices of some chemical graphs such as graphene, coronoid systems and carbon nanocones.
Theoretical calculations involving singlet molecular oxygen (O2(1g)) are challeng- ing due to their inherent multi-reference character. We have tested the quality of re- stricted and unrestricted DFT geometries obtained for the reaction between singlet oxy- gen and a series of alkenes (propene, 2-methylpropene, trans-butene, 2-methylbutene and 2,3-dimethylbutene) which are able to follow the ene-reaction. The electronic en- ergy of the obtained geometries are rened using 3 dierent methods which account for the multi-reference character of singlet oxygen. The results show that the mechanism for the ene-reaction is qualitatively dierent when either one or two allylic-hydrogen groups are available for the reaction. When one allylic-hydrogen group is available the UDFT calculations predict a stepwise addition forming a biradical intermediate, while, the RDFT calculations predict a concerted reaction where both hydrogen abstrac- tion and oxygen addition occur simultaneously. When two allylic-hydrogen groups are available for the reaction then UDFT and RDFT predict the same reaction mechanism, namely that the reaction occurs as a stepwise addition without a stable intermediate between the two transition states. The calculated rate constants are in reasonable agreement with experimental data, except for trans-butene where the calculated rate constant is three orders of magnitude lower than the experimental one. In conclusion we nd that the simple bypassing scheme tested in this paper is a robust approach for calculations of reaction involving singlet oxygen in the limit that the transition state processes low multi-reference character. 2
We present the derivation of a new response method termed rst order po- larization propagator approximation. The electronic structure is given by a density functional representation. We provide a detailed derivation of the method along with explicit expressions for the relevant integrals and matrix elements.
Nuclear Magnetic Resonance (NMR) shielding constants of transition metals in solvated complexes are computed at the relativistic density functional theory (DFT) level. The solvent effects evaluated with subsystem-DFT approaches are compared with the reference solvent shifts predicted from supermolecular calculations. Two subsystem-DFT approaches are analyzed – in the standard frozen density embedding (FDE) scheme the transition metal complexes are embedded in an environment of solvent molecules whose density is kept frozen, in the second approach the densities of the complex and of its environment are relaxed in the “freeze-and-thaw” procedure. The latter approach improves the description of the solvent effects in most cases, nevertheless the FDE deficiencies are rather large in some cases. KEYWORDS — Frozen Density Embedding, NMR shielding constant, solvent shifts, transition-metal complexes
A Majorana fermion is the single fermionic particle that is its own antiparticle. Its dynamics is determined by the Majorana equation, where the spinor field is by definition equal to its charge-conjugate field. In this paper, we investigated Shannon’s entropy of linear Majorana fermions to understand how this quantity is modified due to an external potential of the linear type linear. Subsequently, we turn our attention to the construction of an ensemble of these Majorana particles to study the thermodynamic properties of the model. Finally, we show how Shannon’s entropy and thermodynamic properties are modified under the linear potential action. KEYWORDS: Majorana Fermions; Thermodynamic properties; Shannon’s Entropy.
The vibronic absorption spectrum of Toluidine blue O (TBO) dye in an aqueous solution was calculated using the time-dependent density functional theory (TD-DFT). The calculations were performed using all hybrid functionals supported by Gaussian16 software and 6-31++G(d,p) basis set with IEFPCM and SMD solvent models. The IEFPCM gave underestimated values of λmax in comparison with the experiment, what is a manifestation of the TD-DFT “cyanine failure”. However, the SMD made it possible to obtain good agreement between calculated and experimental spectra. The best fit was achieved using the X3LYP functional. The dipole moments and atomic charges of the ground and excited states of the TBO molecule were calculated. Photoexcitation leads to an increase in the dipole moment of the dye molecule. An insignificant photoinduced electron transfer was found in the central ring of the chromophore of the TBO molecule. Vibronic transitions play a significant role in the absorption spectrum of the dye.
Au nanopyramid particles (Au NBPs) are highly desirable for its remarkable optical properties such as long-range tunable resonance. It has wide applications in room-temperature bioimaging probes and bioanalytical sensors. In this paper, we synthesize Au NBPs with a purity of 95%, and obtain the optical response of Au NBP in near infrared regime. We find that Au NBPs have small mode volume of electric field which can lead to the strong coupling with quantum dots at room temperature. It provides novel applications for Au NBPs in fields of materials, biomedical science, and quantum information
Abstract: In the present work, the geometric structures, the frontier molecular orbitals and the enthalpy of formation (HOF) of thirty six 1, 2, 4, 5-tetrazine derivatives (FTT) were systematically studied by using the B3LYP/6-311+G* method of density functional theory. Meanwhile, we also predicted the stability, detonation properties and thermodynamic properties of all FTT compounds. Results showed that all compounds have superior enthalpy of formation far exceeding that of common explosives RDX and HMX, ranging from 859kJ·mol-1-1532kJ·mol-1. In addition, the detonation performance (Q = 1426cal·g-1 -1804cal·g-1; P = 29.54GPa - 41.84GPa; D = 8.02km·s-1 - 9.53km·s-1), which is superior to TATB and TNT. It is also concluded that the introduction of coordination oxygen on the tetrazine ring can improve the HOF, density and detonation performance of the title compound, and -NH-NH- bridge and -NHNO2 group are also the perfect combination to increase these values. In view of stability, because of the fascinating performance of D3 (ρ =1.89g·cm-3; D = 9.38km·s-1; P = 40.13GPa)，E3(ρ = 1.87g·cm-3; D = 9.19km·s-1; P = 38.35GPa), F1 (ρ = 1.87g·cm-3; D = 9.42km·s-1; P = 40.23GPa) and F3 (ρ= 1.92g·cm-3; D = 9.53km·s-1; P = 41.84GPa), makes them very attractive to be chosen as HEDMs.
It has been a challenge in automated analysis of medical and chemical knowledge to extract represent quantitative structure–activity relationship (QSAR) using intelligent computing in drug discovery. One of many domain-specific bottlenecks in drug discovery is robust conformation search in three-dimensional (3D) space for flexible drug candidates. The process involves researchers and machines working together to achieve their own strengths for greater outcome. The present study has been developing a method for conformational sampling conformers in the class of 4-anilinoquinazoline derivatives for epidermal growth factor receptor (EGFR) tyrosine kinases inhibitors (TKIs). We use AG-1478 to demonstrate how the new intelligent computing method helps to quantum mechanically determine 22 target drug conformer clusters and their properties from conformational sampling, based on density functional theory (DFT) method, time-dependent (TD)-DFT in solvents and clustering analysis (CA). The UV-vis spectra of the preferred conformers agree well with earlier experimental measurements in which the conformer dependent UV-Vis spectral shift of AG-1478 can be as large as approximately 15 nm. We are further developing this method to study and design new 4-anilinoquinazoline derivatives of EGFR TKIs.
Solving numerically a non-Born-Oppenheimer time-dependent Schrödinger equation to study the dissociative-ionization of H2 subjected to strong field six-cycle laser pulses (I = 4 × 1014 W/cm2, λ = 800 nm) leads to newly ultrafast images of electron dynamics in H2+. The electron distribution in H2+ oscillates symmetrically with laser cycle with θ + π periodicity and gets trapped between two protons for about 8 fs by a Coulomb potential well. Nonetheless, this electron symmetrical distribution breaks up for the H2+ internuclear separation larger than 9 a.u. in the field-free region at a time duration of 24 fs as a result of the distortion of Coulomb potential where the ejected electron preferentially localizes in one of the double-well potential separated by the inner Coulomb potential barrier. Moreover, controlling laser carrier-envelope phase θ enables one to generate the highest total asymmetry Aetot of 0.75 and -0.75 at 10○ and 190○, respectively, associated with the electron preferential directionality being ionized to the left or the right paths along the H2+ molecular axis. Thus the laser-controlled electron slightly reorganizes its position accordingly to track the shift in the position of the protons despite much heavier the proton’s mass.
Molecular Dynamics (MD) simulations are widely used to predict the behavior of molecular systems over time. However, one of the great challenges of MD simulations is how to treat the thousands of configurations obtained from calculations, since the number of the quantum calculations (QM) required for evaluating electronic parameters is too high and, sometimes, computationally impracticable. Thus, an efficient and accurate sampling protocol is essential for combining classical MD and QM calculations. In this article, based on the OWSCA methodology, 93 wavelet signals were analyzed in order to further refine the methodology and identify the best wavelet family for [Fe(H2O)6]2+ and [Mn(H2O)6]2+ complexes in solution. Our results point out that the bior1.3 was the best wavelet, values closest to the experimental data were obtained for both studied systems.
The chalcogen vacancy defects in various transition metal dichalcogenides (TMDCs) have been studied using density functional theory (DFT) calculation. Results reveal that (i) the dissociation energy value depends on both nature of chalcogen and transition metal, (ii) the work function depends marginally on the single or double vacancies, (iii) the defect transforms direct band gap to indirect band gap materials (i.e. the pristine materials show KVKC transition whereas defective materials show ΓVKC) and (iii) the d-orbital of the transition metal plays a vital role in the formation of impurity band.
Energetic compounds containing long nitrogen chain, have been a research hotspot. Fused heterocycles are stable due to their aromatic systems. The compound obtained by combining long nitrogen chain and fused ring can not only retain good energetic property, but also ensure better stability. This work designed eight fused heterocycle-based energetic compounds, 3H-tetrazolo[1,5-d]tetrazole (1) and its derivatives (2-8), containing a nitrogen chain with seven nitrogen atoms. The HOF, thermal stability, and energetic properties of these compounds were studied by using the DFT method. The results show that the introduction of -NO2, -N3, -NF2, -ONO2, -NHNO2 groups increased the density, HOF, detonation velocity, and detonation pressure greatly. The densities of 3, 5, 7, and 8 fall within the range designated for high-energy-density materials. The calculated detonation velocity of the compounds 3 and 8 are up to 9.86 km s-1 and 9.78 km s-1, which are superior to that of CL-20. The kinetic study of the thermal decomposition mechanism indicates that the N-R bonds maybe not the weakest bonds of these compounds. The tetrazole ring opening of the heterocycle-based energetic compounds, followed by N2 elimination is predicted to be the primary decomposition channel, whether or not they have substituent groups.
Molecular level insights into the mechanism and thermodynamics of CO oxidation by a (TiO2)6 cluster have been obtained through density functional calculations. Thereby, we have considered as an example, two different structural isomers of (TiO2)6 with the purpose of understanding the interplay between local structure and activity for the CO oxidation reaction. Active sites in the two isomeric forms were identified on the basis of global and local reactivity descriptors. For the oxidation of CO to CO2 we considered both sequential and simultaneous adsorption of CO and O2 on (TiO2)6 cluster through the ER and LH mechanisms, respectively. Three different pathways were obtained for CO oxidation by (TiO2)6 cluster, and the mechanistic route of each pathway were identified by locating the transition-state and intermediate structures. The effects of temperature on the rate of the reaction was investigated within the harmonic approximation. The structure-dependent activity of the cluster was rationalized through reactivity descriptors and analysis of the frontier orbitals. Finally, we also considered the effects of a support, i.e., graphene, on the oxidation mechanism.